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So I have this pair of transmitter and receiver enter image description here

RPI is powered by USB from laptop
Transmitter is connected to Attiny85 being interfaced from RPI at 3v3
Receiver is connected to Arduino at 5v

If I have transmitter VCC connected to RPI 5v, data pin to Attiny85 running at 3.3v and all of them having same ground - all works fine, but obviously range is not great.
At this point same ground connects: transmitter, Attiny, RPI.

So I've tried using external power supply for transmitter.

I have power brick with DC output running at 12v enter image description here
DC output positive goes to VCC, negative to common ground.
At this point same ground connects: transmitter, Attiny, RPI, power brick.
This doesn't work at all, receive nothing.

I have YwRobot breadboard power, which is broken and now supplies 8v on 5v pins enter image description here

I've connected same power brick DC output to YwRobot DC in, positive 5v from board (actually pushing 8v) goes to VCC, negative from board goes to common ground.
At this point same ground connects: transmitter, Attiny, RPI, YwRobot.
This setup transmits data some times, still worse results than connecting VCC to RPI 5v.

Am I missing something? Does external power supply has to be something specific? I've thought as long as grounds are connected any power supply can be used on transmitter.

Update:
This 433MHz transmitter with PCB integrated antenna from my thermostat (powered by 2xAA) has no problem penetrating 3 walls and floor in my house. Sorry for my ignorance, but I need to achieve similar form factor and performance. 2.4GHz modules also require a lot of pins limiting what else can be done with Attiny85. enter image description here

Update:
Attiny is using manchester and software serial (part of Arduino IDE) on attiny core.
RPI is using serial, not sure which version, installed using sudo apt-get install python-serial

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  • Nice powerbank, where did you buy it? It runs about 200USD on amazon. Does it take standard 18650 LiPo cells?
    – user2497
    Mar 18, 2018 at 16:53
  • amazon.co.uk/gp/product/B01DLRGY8A it's enclosed unit
    – goodevil
    Mar 18, 2018 at 21:11
  • That’s an impressive 433 module, I can’t seem to find it on google however. Link?
    – user2497
    Mar 20, 2018 at 21:20
  • Have you got an SDR dongle to verify that data is being transmitted at all? Can you attach an oscilloscope probe to the datapin going to the 433 module? Have you tried receiving on an arduino 168/328p? Have you verified that the attiny has enough RAM free? Are all the pins okay - what does ‘really pushing 8V’ mean? 8V to attiny?
    – user2497
    Mar 20, 2018 at 21:29
  • Data is being transmitted - I connect transmitter and receiver wire directly as they all share same ground. There are no issues with receiver, because by changing power supply to transmitter, receiver starts to receive data. Basically 5v power of GPIO to VCC (transmitter) all good, 8v power of breakout power module to VCC spotty receiving, 12v power of power brick to VCC nothing received. All of them share GND so I'am just switching power cable while module is constant transmitting.
    – goodevil
    Mar 21, 2018 at 20:52

1 Answer 1

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Those 433MHz modules are tricky. I got the best results with 3V3 on the receiver, and 5V on transmitter. You should add an external antenna.

While it would be prudent to remove the little loop antenna, you don’t need to. I got an okay signal at 25 meters with line-of-sight. Metal, or brick will block the signal even at a meter or so - there’s no penetration. Consider a 2.4GHz module for high penetration at low range, or a LoRa module for high range (up to 10km).

A 433MHz antenna I’ve used with good results (can be cut for any frequency really) Ant1

Use the same material for both antenna and radials - copper is good - and optionally stiffen the radials with bicycle spokes on the inside ... make sure there is no electrical contact between the radials and the spokes; tape or heatshrink tube. I found coax cable to suck hard for this application, so I recommend using shielded headphone wire or something similar... just connect the shield to 0V/GND.

As for your breakout power module, I’ve had the same issue. Those modules are dangerous, avoid them. Use 7805 and LM1117 instead. Or just one 5V source (your powerbank?) and a TO-92 LM317 set to 3V3 output (max 100mA). Tiny 3V step-down converters like this can supply 800mA. https://m.banggood.com/5V-To-3_3V-DC-DC-Step-Down-Power-Supply-Buck-Module-AMS1117-800MA-p-933674.html ( you can find them a lot cheaper )

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  • My project is home automation setup, so 433MHz is preferred as 2.4GHz is so crowded and adding another 4 low-powered devices wouldn't improve situation. I've ordered these ebay.co.uk/itm/172936544379 to try out, but thing is, my current 433MHz still should work with very small antenna within the house. I've dissembled my current thermostat and it has similar 433MHz transmitter with tiny coiled antenna and have no problem connecting to boiler across whole house. I already have external antennas from multi-thread cable, but will try to get some solid copper wire for testing.
    – goodevil
    Mar 18, 2018 at 21:10
  • @goodevil You will not penetrate even a finger with these modules... the 2.4GHz modules have ways to mitigate band saturation - else look at 860/900MHz.
    – user2497
    Mar 18, 2018 at 21:12
  • I've update my question - as similar size device is able to achieve what I need
    – goodevil
    Mar 18, 2018 at 21:53
  • With my current setup I am ALREADY penetrating wall and floor, adding another wall makes receiving spotty and taking receiver even further, prevents it from receiving anything. I've update my question - as similar size device is able to achieve what I need, I assume I just missing something in my setup. nRF24L01 would leave my Attiny with no available pins, or in best case with 2 pins, which is my plan B if I can't replicate performance of current thermostat.
    – goodevil
    Mar 18, 2018 at 22:03
  • @goodevil What library are you using?
    – user2497
    Mar 18, 2018 at 22:03

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